Investigations are being conducted on the involvement of the renin-angiotensin system and prostaglandins on control of vascular tone in anesthetized and unanesthetized dogs. Prostacyclin release has been demonstrated in the canine skeletal muscle vascular bed and its role in this bed is being studied. The possible association of prostaglandin E release with the renal vasodilator response to the converting enzyme inhibitor captopril is being examined in both the anesthetized and unanesthetized dog. Experiments along the same line with other agents which block the renin-angiotensin system are also being carried out. Pump-perfusion of the canine kidney has been found to cause a progressive release of renin and prostaglandin E, and the net effect is to decrease the dog's systemic arterial blood pressure. The mechanism of prostaglandin E release under these conditions is being studied.